Electrical heating apparatus



* Oct. 2, 1945.

W, M. WlTTY ELECTRICAL HEATING APPARATUS Filed June 30, 1943 PatentedOct. 2, 1945 i 2,385,904 ELECTRICAL HEATING APPARATUS William M. Witty,Haddonlield, N. J., assignor to Radio Corporation of America, acorporation o! Delaware Application June 30, 1943, Serial No. 492,821

(Cl. 21S-13) 13 Claims.

This invention relates to electrical heating aplparatus, and moreparticularly to apparatus for heating electro-conductive articles byinduction with the aid ci high frequency electrical energy.

many industrial applications, it is necessary, during the manufacture oivarious articles, to apply heat thereto. in some cases, it is desirableto apply the heat only locally and with i'air ram pidity. @ne suchexample is in the case of ca pacitor cans comprised ci a receptacle anda cover which is soldered thereto.

lit has been proposed, heretofore, to employ radio frequency energy' forheating electro-corr ductive articles cy induction. ln accordance withcustomary practice employing radio frequency energy, applicator coils orinductors are used which are placed around the Work, particularly Wherethe Work is small. An arrangement or' this sort is obviously unsalted toa continuous heating operation AWhere a plurality of articles are to beheated, as in conveyor 'belt operation.

The primary object of my invention is to provide an improved apparatus`ior applying radio freoueocy energy inductivcly to a succession ofdiscrete articles to ce heateda More particularly, .it is an object cimy oreserit invention to provide an imoroved apparatus for inductivelyheating electro-ccnductive articles hy means of radio frequency enerowhich apparatus is highly suitable for high speed production incontinuous operations.

' another object ci my present invention to provide ari improvedapparatus as aforesaid which is particularly suited the application oi'radio frequency induction heating to effect soldering.

gialli another object of my present iiivcticn is to provide an improved.inductive heat'. g acparatus by means ci? which electrical energy loeapplied erilcierltly to the articles to ice 'treated during manufacturefor purpose ci selectively generating 'heat within the articles Whilethey are moved. along continuously on a conveyor belt.

il further object of my 'present invention is to provide improvedinductive heating apparatus as above set iorth wherein the leakagereactance reduced to a minimum.

Still a further object of my present invention is' to provide improvedinductive heating apparatus as above set forth which is inexpensive incost and in operation, and which is extremely efficient in use.

In accordance with the present invention, I make use of specially shapedinductor devices as applicators which form the load coupling circuit ofa radio frequency generator and obtain thereby very eiicierrt couplingto the articles which are lto be selectively heated, as for soldering orthe v one form of my present invention, the inductors may be constitutedby elongated conductors the ends of which are onset with respect to thebody portion, with the ends constituting very short leads for connectionto the transformer. This, together with 'the fact that the two inductorsare connected together electrically in. parallei relation as iar as thegenerator is concerned, results in less effective leakagey reactance;and

this, inturn, together with the efect'of series coupling insofar as theload is concerned; resuits in a very high percentage of overallerliciency.

The novel features 'that I consider characteristic of my invention areset iol-th with particuiarity in appended claims. The invention itself,however, Yoo'th as to its organization and method of operation, as wellas additional objects and advantages thereof, will best "ce understoodtrom the following description of one emhoclimerot thereof, when read inconnection with 'the accompanying drawing in which:

Figure i is a perspective View ci one form o11 heating device o untconstructed in accordance 'with my invention,

Figure 2 is a similar View but showing, in acldition, a portion of theendless conveyor and one unit of the work thereon in relation to theheating device,

L'ilgure 3 is an enlarged, fragmentary sectional view taken on the lineIl I--III of Figure 2. and

Figure a is a wiring diagram showing the connection of the couplinginductors to the transformer and the relation of the inductors to thework.

Referring more particularly to the drawing wherein similar referencecharacters designate corresponding parts throughout, there is shown atubularrsupporting member l of insulated material on which is Wound theprimary Winding 3 las a vacuum 'tube oscillator.

of a transformer coupled to a suitable high irequency oscillationgenerator (not shown), such Surrounding the primary winding 3 and spacedtherefrom by plurality of circumferentially distributed, longitudinallydisposed, insulated spacing members 5 is a single turn secondary windingfl of copper sheet material. The ends 'Ia and lb of the in eachinstance.

l aseaeoa for the purpose of uniting the cover` to the case Closemagnetic coupling be- Jtween the work l@ and the inductors Il and ISsecondary Winding I are bent outwardly to form a pair of spaced,terminal members, and they are formed, respectively, adjacent one endwith the slots 9a and 9b.

Connected to the secondary winding terminals Ia and Ibare a pair ofinductor coupling devices 1 or applicators I I and I3 by means of whichheating currents are induced in the work in the manner shortly to bedescribed. The applicators or devices Il and i3 are constituted byconductors having elongated, intermediate body portionsv Ita and i3dformed with substantially right angle bends IIb and lb. The bodyportions lla and Ita are disposedphysically in spaced relation and arearranged generally parallel to each other. Beyond the bends IIb and lh,the applicators are formed with reverse or U-bends IIc and 53o toprovide end portions which are disposed in substantially parallel planesapproximately at right angles to the plane in which the body portionsIIa and I3a`lie. As best' seen from Figure 1, the Inductor or applicatorI I is connected at one end to the terminal la, its other end passingthrough. the slot 9a without contacting the terminal 'lo and beingconnected to the terminal 1b. Similarly, the inductor or applicator I3is connected at one end to the terminal Il?, its other' end passingthrough the opening 9b out 'of contact with the terminal 'Ib and beingconnected to the terminal 1a. Thus,

i the two inductors I I and \I3 are not only arranged in physicallyparallelrelation relative to each other, but are also connected inparallel relation electrically across the secondary winding as will benoted from Figure 4. Y v Betweenthe loopsformed by the U-bends IIc andI3c, there `is movably carried'an endless conveyor belt I5. A pluralityof insulated receptacles I'I are secured to the belt I 5, as by means ofrivets l' ,I8 (only one receptacle beingshown in the drawing by way ofillustration). 'I'he receptacles I1 are so dimensioned that the sidesthereof will be is obtained by reason of the fact that the recep= taclesIl are in close proximity to the inductors.

Since the inductors II and I3 are so connected to the secondary winding'i that currents will ow therein in opposite directions instantaneously,as represented by the arrows A and B of Figure 4, it is apparent thatthe currents A and B will induce in the load constituted by each of thework units 'I9 currents represented by arrows l C and D. Because thecurrents C and D are in series,I it is apparent that they will becumulative or additive in effect. Moreover, since the leadsconstituted-by the U-bendsv lic and i3@ which connect the body portionslla and' lila of the inductors to the secondary terminals la and Eb arevery short, the leakage reactance will be reduced to a minimum. Thisfactor, teken with the'serles coupling ot the inductors insofar as theload is concerned, results `in a v ery high percentage of overallemcienoy.

From the foregoing description, it will be apparent that my improvedvheating apparatus affordsran arrangementfo'r heating the Work on anendless conveyor set-up with great emciency.

The speed of the conveyor belt I5 and the power input into the workwill, of course, depend uponl various factors, such as the rate at whichan operator can load the work, the lengths of the inductors I I. and I3,the temperature towhich it is desiredto bring the work, etc. In oneinstalladisposedA in as close proximity to the body portions 1 of theinductors II and I3 as is feasible while the receptacles il are beingadvanced between the inductors by the'endless belt l5. Each of thevreceptacles Il is adapted to 'work units i9.

receive one or rnore- By Way of illustration, the Work units i9 havebeen shown as constituted by capacitor cans of conducting material andcomprised of -a case 59a to which a bottom cover ith/is to be secured.For this purpose, the inner surface or" the bottom teli, oriowervpvortion oi the outer surface of the case ita, or both, may becoated. with a layer of relatively low melting point solder iii. Duringe...

tion, for example, where the work wasloaded lat a rate of about 2500units per hour, whe're the inductors l I and I3 were approximately sixinches in length. and where 4 kw. of power were delivered to theinductors at a frequency 'of 350 kc. per second; the belt I6 wasadvanced at a rate of about 20 feet per minute. In this particularinstallation, the inductors II and I3 and the .primary winding 3 wereall made of copper tubing through which water was passed for cooling.

Although I have shown and described but one embodiment. of my invention,it will undoubtedlybe apparent to those skilled in the art that desirethat my invention shall not be limited except insofar as is madenecessary by the prior art and by the spirit of the appended claims;-

I claim as my invention: L f

l. in inductive heating apparatus, the combination of al pair ofinductor coupling devices disposed one along eachside of a predeterminedpath with the maior portion of their lengths extending along at least aportion o,f"said path, means for coupling said devices to asource oihigh frequency electrical energy, means connecting saiddevices to saidilrst 'named means in parallel relation electrically and providing asmali leakage reactance, and a movable carrier arranged for movementalong said path adjacent to said devices, Said carrier being adapted tosupport a plurali' of electro-conductive work units i and to more saidunits in succession one said pa in inductive relation to each oi ddevices, a c current passed through both said as hey are advanced alongmotive heat"z ng apparato r' @t L" induce heating current tending alongat least a portion of said path,

means for coupling said devices to a source of high frequency electricalenergy, means providing a small leakage reactance connecting saiddevices to said first named means inv parallel relation electrically insuch a manner that current will flow throigh said devicesinstantaneously in opposite directions, and a movable carrier arrangedfor movement along said path adjacent to said devices, said carrierbeing adapted to support a, plurality of electro-conductive Work unitsthereon and to move said units in succession along said path ininductive relation to said devices, the current passed through saiddevices serving to induce heating current in said units as they areadvanced along said path.

3.'Heating apparatus according to claim 2 wherein said inductor couplingdevices include short leads whereby they are connected to said means.

4. Heating apparatus according to claim 2 wherein said inductor couplingdevices are comprised of relatively elongated members disposed inphysically parallel relation, said members terminating in relativelyshort offset portions constituting leads for connection thereof to saidmeans. n

5. Heating apparatus according 'to claim 2 characterized by the additionof a plurality of work supporting members on said carrier, each adaptedto receive at least one of said work units.

6. Heating apparatus according to claim 2 characterized by the additionof a plurality of Work supporting members secured to said carrier andeach adapted to receive at least one of said work units, andcharacterized further in that said work supporting members are soarranged on said carrier as` to be in close proximity to said inductorcoupling devices as said members are advanced along said path whereby toeffect close magnetic coupling between said devices and the units insaid members.

7. In inductive heating apparatus, the combination of a transformer ofwhich the primary winding is adapted to be connected to a source of highfrequency electrical. energy, a pair of .l

inductor coupling devices, means connecting said inductor couplingdevices in electrically parallel relation across the terminals of thesecondary winding of said transformer and providing a small leakagereactance, said devices comprising a pair of elongated conductorsdisposed in physically parallel, spaced relation along at least aportion of a predetermined path with the major portion of their lengthsextending parallel to said -path portion, and a movable conveyor adaptedto support a plurality of electro-conductive work units arranged formovement along said path to advance said units through the space betweensaid devices and in close proximity thereto whereby to bring said unitssuccessively intoinductive relation with each of said devices.

8. Heating apparatus according to claim 'I characterized in that saidconveyor is constituted by an endless belt.

9. Heating apparatus according to claim 7 characterized in that saidconveyor is constituted by an endless belt, and characterized further bythe addition of a plurality of work receiving receptacles secured tosaid belt, said receptacles being of such dimensions and being sodisposed ony said belt that the sides thereof are in close proximity tosaid conductors while they are being moved through said space.

10. In inductive heating apparatus, the combination of a movablecarrier, a plurality of work supporting elements mounted on said carrierand adapted to be moved through an endless path thereby, a Apair ofinductor devices disposed in physically parallel relation one on eachside of said path with the major portion of their lengths extendingalong at least a portion of said path whereby said elements will bemoved between said devices, said devices being also connected inparallel relation electrically, means for coupling said devices to asource of high frequency energy, and means providing a' small leakagereactance connecting said devices to said coupling means.

11. In electrical heating apparatus, the combination of a transformerhaving a multi-turn primary winding and a single-turn, conductive,sheet; member inductively related to said primary winding andconstituting the secondary winding of said transformer, said secondarywinding having a single pair of output terminals, and a pair of inductorcoupling members connected i'n parallel relation electrically acrosssaid secondary Winding output terminals, said members each comprising anelongated conductor having its end portions offset from the bodythereof, and the terminals of said end portions being connected to saidsecondary winding output terminals.

12. In electrical heating apparatus, the combination of a transformerhaving a multi-tum primary winding and a single-turn, conductive, sheetmember inductively related to said primary winding and constituting thesecondary winding of said transformer, said secondary winding having asingle pair of elongated output terminals,

and a pair of inductor coupling members connected in parallel relationelectrically across said secondary winding output terminals, saidmembers each comprising an elongated conductor disposed along a separateone of said elongatedfoutput terminals and having its end portionsoifset from the body thereof, and the terminals of said end portionsbeing connected tovsaid secondary winding output terminals.

13. An inductor coupling device comprising an elongated conductor havingend portions bent substantially at right angles to the body portionthereof, said end portionsy having reverse bends in parallel planeseachsubstantially normal to said body portion, and said reversely bentportions extending generally inthe same direction.

